Diffusion welding in air

ABSTRACT

Solid state welding a butt joint by fusion welding the peripheral surfaces to form a seal, autogenetically cleaning the faying or mating surfaces of the joint by heating the abutting surfaces to 1,200*C., and heating to the diffusion welding temperature in air.

United States Patent [1 1 Moore et a1.

m1 3,787,959 i451 Jan. 29, 1974 DIFFUSION WELDING IN AIR [75] Inventors: Thomas J. Moore, Berea; Kenneth H. Holko, Strongsville, both of Ohio [73] Assignee: The United States of America as represented by the Administrator of the National Aeronautics and Space Administration, Washington, DC.

221 Filed: Apr. 24, 1972 211 Appl. No.: 247,090

[52] US. Cl 29/482, 29/488, 29/497, 29/498 [51] Int. Cl B23k 31/02 [58] Field of Search.. 29/488, 497, 497.5, 482, 498, 29/494, 486

[56] References Cited UNITED STATES PATENTS 3,101,532 8/1963 Christensen 29/497 X 3,195,229 7/1965 Culver 29/497 X 3,235,957 2/1966 Horsting 29/497.5 X 3,393,445 7/1968 Ulam 29/497.5 X 3,400,449 9/1968 Maguire et a1 29/488 X 3,468,016 9/1969 Lorain et a1. 29/488 Primary ExaminerRichard' B. Lazarus Attorney, Agent, or FirmN. T. Musial et a1.

[5 7] ABSTRACT Solid state welding a butt joint by fusion welding the peripheral surfaces to form a seal, autogeneticaily cleaning the faying or mating surfaces of the joint by heating the abutting surfaces to 1,200C., and heating to the diffusion welding temperature in air.

8 Claims, 6 Drawing Figures PAIENTEB JAN 2 9 lSM SHEET 2 BF 3 Grind s u rfaces Deg rease su rlaces Assemble Tack weld

Seal

weld

Auto-vac seal Solid state weld FIG. 4

PATENTEDJANZQ m4 3,787. 959

SHEET 3 BF 3 FIG. 5

DIFFUSION WELDING IN AIR ORIGIN OF THE INVENTION The invention described herein was made by employees of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment, of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention is concerned with solid state welding in air. The invention is particularly directed to diffusion welding without using a vacuum furnace or a hot press.

Fusion welding presently is widely used. In fusion gwelding the edges of the parts to be welded are melted. Various arc-welding methods are used to fusion weld steel plates. For fusion welding heavier sections, elec- SUMMARY OF THE INVENTION These problems have been solved by the present invention wherein surfaces of parts to be welded are brought together at a butt joint. A seal weld is formed around the periphery of the butt joint, and autogenous faying surface cleaning is used. Diffusion welding is obtained by heating the assembly in air with deadweight loading.

OBJECTS OF THE INVENTION It is, therefore, an object of the present invention to provide a method of solid state welding without deformation which can be used with thick sections.

Another object of the invention is to provide a method of welding which utilizestem'peratures well below the melting temperature of the material being welded.

Another object of the invention is to provide a method of diffusion welding metal which does not require conventional vacuum hot press equipment.

These and other objects of the invention will be apparent from the specification which follows and from the drawing wherein like numerals are used throughout to identify like parts.

DESCRIPTION OF THE DRAWING FIG.- 1 is an elevation view showing two members which are to be solid state welded in accordance with the present invention;

FIG. 2 is an elevation view partially in section showing the members assembled in preparation for welding in accordance with the invention;

FIG. 3 is an elevation view of the assembled members being welded;

FIG. 4 is a flow sheet illustrating diagrammatically the preferred process for solid state welding in accordance with the present invention; and

FIGS. 5 and 6 are XSOO-photomicrographs of diffusion welds made in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing there is shown in FIG. 1 a pair of members 10 and 12 which are to be solid state welded together in accordance with the present invention. The member '10 has a surface 14 which faces a similar surface 16 on the member 12.

By way of example test plates 10 and 12 of A18] 1020 steel have been diffusion welded in accordance with the present invention. It is contemplated the invention can be modified for welding mild steel and stainless steel. Reactive and refractory metals that can dissolve in their own oxides can also be welded in accordance with the invention.

The process may be adapted for welding nickel-base alloys. It isfurther contemplated the process can be used for welding nonmetals, such as ceramic and glass. The surfaces 14 and 16 shown in FIG. I are prepared for welding as shown in the flow sheet of FIG. 4. Where the members 10 and 12 are metal the surfaces 14 and 16 are ground. By way of example, the surfaces 14 and 16 of the AIS] .1020 steel plates were ground to about a 40.7Xl0cm rms (l6 rms) finish. The finish ground surfaces were protected by applying a coating of oil.

The faying surfaces 14 and 16 are cleaned immediately prior to assembling the members 10 and 12 in the position as shown in FIG. 2. This cleaning is accomplished by wiping the surfaces with acetone and then alcohol. These solvents are particularly useful in removing grease.

The members 10 and 12 are then assembled in the position shown in FIG. 2. The faying surfaces 14 and 16 are in contact to form a butt joint. The members are held in the position shown in FIG. 2 with suitable clamps.

The members are tack welded at 18 and the clamps are removed. A seal weld 20 is formed on the periphery of the faying surfaces 14 and 16. By way of example, the SMA welding process was used successfully for both the tack welds and the seal welds. 3.2mm (1/8 inch) diameter AWS-El8 covered electrodes were used. In the case of diffusion weldingPH' nickel-base materials, it is contemplated that the faying surfaces 14 and 16 would be cleaned and .coated with a thin deposit of nickel or other suitable material prior to seal welding at the edges. I

The faying surfaces 14 and 16 of the seal welded assembly shown in FIG. 2 are cleaned by the use of an autogenous or self-generated surface cleaning principle. This is designated as auto-vac cleaning and is used to reduce the effects of. surface oxides that would normally hinder diffusion welding. During auto-vac cleaning'the oxides and gases are dissolved in the parent metal.

In this procedure the seal welded assembly shown in FIG. 2 is placed in an air-atmosphere, resistanceheated furnace 22. The seal welded assembly is then heated to an elevated temperature for a time sufficient to clean the surfaces 14 and 16. The seal welded cleaned assembly is then cooled to ambient temperature within the furnace. By way of example, successful auto-vac cleaning was achievedby utilizing a temperature of 1,200C for 2 56 hours.

The cleaned seal welded assembly is again placed in the resistance-heated air-atmosphere furnace 22. A deadweight 24 is applied to the assembly as shown in FIG. 3. By way of example, a deadweight loading of about 5 psi was used with the aforementioned test samples. It is further contemplated that atmospheric pressure due to auto-vac cleaning could produce additional pressure on the joint.

The assembly of test plates was heated in the furnace 22 at three diffusion welding temperatures: 1,200C, l,090C, and 980C. Table I shows the mechanical properties of diffusion welds in the aforementioned specimens at these temperatures. The welding pressure for each test was 3.45X N/m or 5 psi. The diffusion welding time for each specimen was two hours. 7 All weldments in Table l were double normalized at 900C prior to testing. The tensile specimen axis and long side of the bend specimens were parallel to the short-transverse direction in the parent metal'plate in the first weldment. They were parallel to the transverse direction in the parent metal plate in the other three weldments.

A study of Table I shows that with a seal weld at the joint periphery a sound, strong diffusion weld can be produced in air. This is illustrated by the bend data shown in the last column. For sealed assembly No. l diffusion welded at 1,200C, preweld auto-vac cleaning was not necessary because both cleaning and diffusion welding took place in the two hour weld time at this temperature. FIG. 5 is a photomicrograph of this weld.

Sealed weldment No. 2 which was diffusion welded at 1 )90C with preweld auto-vac cleaning at 1,200C,

was successfully bent 180. FIG 367s a photomicrograph of this weld. weldment No. 3 which was also welded at l,090C but not auto-vac cleaned, failed the bend test at 5. Thus pre-weld auto-vac cleaning plays a major role in subsequent l,090C diffusion welding.

Sealed weldment No. 4 had excellent tensile properties but failed the bend test at 45". This indicates that the weldin temperature of 980C is not sufficiently high to produce full parent metal properties at the diffusion weld.

Ch, that serves to absorb gases. The getter, in the form of wire, is placed at the periphery of the weld joint under the seal weld.

What is claimed is:

l. A method of solid state welding a pair of members together in air comprising the steps of;

forming substantially flat faying surfaces on said members,

assembling said members together'with said faying surfaces in contact,

forming a seal weld about the periphery of said faying surfaces of said assembled members,

cleaning said faying' surfaces by heating said seal welded assembly to an elevated temperature of 1,200C whereby gases and oxides between said faying surfaces are dissolved in said members, said seal weld'preventingsaid air atmosphere from entering the space between said faying surfaces and whereby said cleaning is accomplished without applying any external pressure,

applying pressure up to about 5 psi to said faying surfaces by deadweight loading, and

diffusion welding said faying surfaces without macroscopic deformation by heating the cleaned seal weld assembly to an elevated temperature from 980C to 1,200C while applying said pressure.

2. A method of solid state welding as claimed in claim I wherein the faying surfaces are formed by grinding.

3. A method of solid state welding as claimed in claim 2 including the step of applying a coating of oil to the ground faying surfaces prior to assembly.

4. A method of solid state welding as claimed in claim 3 including the step of removing the oil coating immediately prior to assembly.

5. A method of solid state welding as claimed in claim 1 including the step of tack welding the assembled I members at the periphery of said faying surfaces prior PROPERTIES OF DIFFUSION WELDS Tensile tests Auto-vac Diffusion cleaning Welding Yield strength Tensile strength Elonga- Reduction temperature, temperature, tion. in-area, Fracture Guided "C I, .C MN/m ksi MN/m ksi percent percent location bend 1200 310 44.9 495 71.8 20 30 Parent metal 180.

304 44.1 503 72.9 22 3 1090 238 34.5 455 65.9 42 180. 227 32.9 454 65.7 36 1090 298 43.3 368 53.3 6 Fracture at 269 39.0 1 weld at 5. 980 231 33.5 454 65.7 35 ractu'r'e at 233 33.7 442 64.1 32 weld at 45.

7. A method of solid state welding as claimed in claim 1 including the step of;

cooling the seal welded assembly after cleaning and before diffusion welding. 8. A method of solid state welding as claimed in claim 7 wherein the faying surfaces are cleaned by heating to a temperature of about 1,200C for about 2 5: hours,

and diffusion welded by heating to a-temperature of about l,090C for about 2 hours.

. F t It! 

1. A method of solid state welding a pair of members together in air comprising the steps of; forming substantially flat faying surfaces on said members, assembling said members together with said faying surfaces in contact, forming a seal weld about the periphery of said faying surfaces of said assembled members, cleaning said faying surfaces by heating said seal welded assembly to an elevated temperature of 1,200*C whereby gases and oxides between said faying surfaces are dissolved in said members, said seal weld preventing said air atmosphere from entering the space between said faying surfaces and whereby said cleaning is accomplished without applying any external pressure, applying pressure up to about 5 psi to said faying surfaces by deadweight loading, and diffusion welding said faying surfaces without macroscopic deformation by heating the cleaned seal weld assembly to an elevated temperature from 980*C to 1,200*C while applying said pressure.
 2. A method of solid state welding as claimed in claim 1 wherein the faying surfaces are formed by grinding.
 3. A method of solid state welding as claimed in claim 2 including the step of applying a coating of oil to the ground faying surfaces prior to assembly.
 4. A method of solid state welding as claimed in claim 3 including the step of removing the oil coating immediately prior to assembly.
 5. A method of solid state welding as claimed in claim 1 including the step of tack welding the assembled members at the periphery of said faying surfaces prior to seal welding.
 6. A method of solid state welding as claimed in claim 1 wherein the faying surfaces of the seal welded assembly are cleaned by heating to 1,200*C for about 2 1/2 hours.
 7. A method of solid state weldinG as claimed in claim 1 including the step of; cooling the seal welded assembly after cleaning and before diffusion welding.
 8. A method of solid state welding as claimed in claim 7 wherein the faying surfaces are cleaned by heating to a temperature of about 1,200*C for about 2 1/2 hours, and diffusion welded by heating to a temperature of about 1090*C for about 2 hours. 